Devices for imaging body cavities or passages in vivo are known in the art and include endoscopes and autonomous encapsulated cameras. Endoscopes are flexible or rigid tubes that pass into the body through an orifice or surgical opening, typically into the esophagus via the mouth or into the colon via the rectum. An image is formed at the distal end using a lens and transmitted to the proximal end, outside the body, either by a lens-relay system or by a coherent fiber-optic bundle. A conceptually similar instrument might record an image electronically at the distal end, for example using a CCD or CMOS array, and transfer the image data as an electrical signal to the proximal end through a cable. Endoscopes allow a physician control over the field of view and are well-accepted diagnostic tools. However, they do have a number of limitations, present risks to the patient, are invasive and uncomfortable for the patient, and their cost restricts their application as routine health-screening tools.
Because of the difficulty traversing a convoluted passage, endoscopes cannot reach the majority of the small intestine and special techniques and precautions, that add cost, are required to reach the entirety of the colon. Endoscopic risks include the possible perforation of the bodily organs traversed and complications arising from anesthesia. Moreover, a trade-off must be made between patient pain during the procedure and the health risks and post-procedural down time associated with anesthesia. Endoscopies are necessarily inpatient services that involve a significant amount of time from clinicians and thus are costly.
An alternative in vivo image sensor that addresses many of these problems is capsule endoscope. A camera is housed in a swallowable capsule, along with a radio transmitter for transmitting data, primarily comprising images recorded by the digital camera, to a base-station receiver or transceiver and data recorder outside the body. The capsule may also include a radio receiver for receiving instructions or other data from a base-station transmitter. Instead of radio-frequency transmission, lower-frequency electromagnetic signals may be used. Power may be supplied inductively from an external inductor to an internal inductor within the capsule or from a battery within the capsule.
An autonomous capsule camera system with on-board data storage was disclosed in the U.S. patent application Ser. No. 11/533,304, entitled “In Vivo Autonomous Camera with On-Board Data Storage or Digital Wireless Transmission in Regulatory Approved Band,” filed on Sep. 19, 2006. This application describes a capsule system using on-board storage such as semiconductor nonvolatile archival memory to store captured images. After the capsule passes from the body, it is retrieved. Capsule housing is opened and the images stored are transferred to a computer workstation for storage and analysis. For capsule images either received through wireless transmission or retrieved from on-board storage, the images will have to be displayed and examined by diagnostician to identify potential anomalies.
Besides the above mentioned forward-looking capsule cameras, there are other types of capsule cameras that provide side view or panoramic view. A side or reverse angle is required in order to view the tissue surface properly. Conventional devices are not able to see such surfaces, since their FOV is substantially forward looking. It is important for a physician to see all areas of these organs, as polyps or other irregularities need to be thoroughly observed for an accurate diagnosis. Since conventional capsules are unable to see the hidden areas around the ridges, irregularities may be missed, and critical diagnoses of serious medical conditions may be flawed. A camera configured to capture a panoramic image of an environment surrounding the camera is disclosed in U.S. patent application Ser. No. 11/642,275, entitled “In vivo sensor with panoramic camera” and filed on Dec. 19, 2006. The panoramic camera is configured with a longitudinal field of view (FOV) defined by a range of view angles relative to a longitudinal axis of the capsule and a latitudinal field of view defined by a panoramic range of azimuth angles about the longitudinal axis such that the camera can capture a panoramic image covering substantially a 360 deg latitudinal FOV.
Conceptually, multiple individual cameras may be configured to cover completely or substantially a 360 deg latitudinal FOV. However, such panoramic capsule system may be expensive since multiple image sensors and associated electronics may be required. A cost-effective panoramic capsule system is disclosed in U.S. patent application Ser. No. 11/624,209, entitled “Panoramic Imaging System”, filed on Jan. 17, 2007. The panoramic capsule system uses an optical system configured to combine several fields-of-view to cover a 360° view. Furthermore, the combined fields-of-view is projected onto a single sensor to save cost. Therefore, this single sensor capsule system functions effectively as multiple cameras at a lower cost.
Similar to the situation with a conventional forward looking capsule system, for side-view and panoramic view capsule systems with digital wireless transmission or on-board storage, the captured images will be played back for analysis and examination. During playback, the diagnostician looks to find polyps or other points of interest as quickly and efficiently as possible. The playback is at a controllable frame rate and may be increased to reduce viewing time. However, if the frame rate is increased too much, the gyrations of the field of view (FOV) will make the video stream difficult to follow. At whatever frame rate, image gyration demands more cognitive effort on the diagnostician's part to follow, resulting in viewer fatigue and increased chance of missing important information in the video.
For images associated with either a conventional capsule camera with forward-looking view, a capsule camera with side view or a panoramic camera with a panoramic view, the images will be viewed by diagnostician on a viewing station or a display device. Due to the large amount of image data to be examined and the cost associated with the diagnostician's time, it is desired that the video corresponding to the image data can be displayed in a way that will help reduce the diagnostician viewing time without compromising the quality and reliability of the diagnostics.